Method for retrieving a lost tool in a borehole using an acoustical well sounder

ABSTRACT

A method is disclosed using an overshot retrieving device which is lowered into a borehole by means of tubing until the overshot arrives at a lost tool. An attempt is made to engage the tool with the overshot and after the attempt the overshot is raised a predetermined distance. An acoustical well sounder provides a soundwave in the tubing. When the overshot has successfully engaged the lost tool, the recorder of the well sounder provides a recording having a primary deflection in one sense in response to a reflection of the soundwave to indicate that the tool has been engaged. When the overshot has not engaged the tool, the reflection of the soundwave causes the recording to have a primary deflection in an opposite sense to indicate that the tool has not been engaged. An operator may then remove the overshot, the lost tool and tubing or repeat the engagement operation in accordance with the record provided by the recorder.

nited States Patent Tanner METHOD FOR RETRIEVING A LOST TOOL IN A BOREHOLE USING AN ACOUSTICAL WELL SOUNDER 1 1 Jan. 25, 1972 [57] ABSTRACT A method is disclosed using an overshot retrieving device which is lowered into a borehole by means of tubing until the overshot arrives at a lost tool. An attempt is made to engage the tool with the overshot and after the attempt the overshot is raised a predetermined distance. An acoustical well sounder provides a soundwave in the tubing. When the overshot has successfully engaged the lost tool, the recorder of the well sounder provides a recording having a primary deflection in one sense in response to a reflection of the soundwave to indicate that the tool has been engaged. When the overshot has not engaged the tool, the reflection of the soundwave causes the recording to have a primary deflection in an opposite sense to indicate that the tool has not been engaged. An operator may then remove the overshot, the lost tool and tubing or repeat the engagement operation in accordance with the record provided by the recorder.

8 Claims, 5 Drawing Figures PATENTED JANZS i972 SHEET 1 OF 2 gww FIG. 3

FIG. 2

FIG. 1

PATENTEDJANZSTQYZ 3.637.038

SHEET 2 0F 2 START OF END OF NEGATIVE PRIMARY TUBING TUB|NG a DEFLECTION FIG. 4

WITH TOOL POSITIVE PRIMARY DEFLECTIQN START END OF TUBING OF 1 8| OVERSHOT TUBING WITHOUT TOOL FIG. 5

METHOD FOR RETRIEVING A LOST TOOL IN A BOREHOLE USING AN ACOUSTICAL WELL SOUNDER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for retrieving a lost tool in a borehole and, more particularly, to retrieving a lost tool with an overshot retrieving device.

2. Description of the Prior Art Heretofore, when attempting to retrieve a lost tool at the bottom of a borehole, it could not be determined if the overshot had engaged the tool without removing the retrieving device from the borehole. When the tool is stuck in the borehole, the weight indicator at the borehole may be used to indicate if the tool has been engaged since the required lifting force is equal to the weight of the tool and the force required to break the tool loose. However, the weight indicator cannot be used when the tool is lying free at the bottom of the borehole because the weight indicator is insensitive to the weight of the tool alone.

Since it could not be determined if there was an engagement of the tool at the bottom of the borehole, the overshot has to be removed from the borehole after each attempted engagement. The removal of the overshot and its associated tubing from the borehole without the lost tool may in many instances require the pulling of thousands of feet of tubing. The removal of the overshot without the tool is therefore extremely costly.

Although the problem of engaging a lost tool at the bottom of a borehole and the acoustical well sounder have been in existence for many years, the acoustical well sounder had not been used to solve the problem until the method of the present invention was conceived.

Heretofore, the acoustical well sounder provided records relating to the depth of the borehole or the level of a fluid in the borehole. It is not obvious from the many patents covering acoustical well sounders, such as US. Pat. No. 2,560,91 I, that an acoustical well sounder may be used to determine whether or not a retrieving device has engaged a lost tool in a borehole. Furthermore, it is not obvious from the patents or from literature describing acoustical well sounders how an acoustical well sounder may be connected and operated to determine whether or not a retrieving device has engaged the lost tool.

SUMMARY OF THE INVENTION A method for retrieving a tool lost in a borehole in which a retrieving device with tubing is inserted into the borehole. An attempt is then made to have the retrieving device engage the tool. The retrieving device is then withdrawn a predetermined distance and a sound wave is provided in the tubing. A reflection of the sound wave is monitored to determine whether or not the retrieving device has engaged the tool. When the retrieving device has engaged the tool, the retrieving device, the tool, and tubing are removed from the borehole.

One object of the present invention is to provide a method for retrieving a tool lost in a borehole with an overshot retrieving device in which it is determined if the overshot has engaged the lost tool while the overshot is still in the borehole.

Another object of the present invention is to provide a method for retrieving a tool lost in a borehole with an overshot retrieving device and tubing in which an acoustical well sounder is used to determine if the overshot has engaged the lost tool.

The foregoing and other objects and advantages will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. I, 2, and 3 are pictorial representations of structural arrangements occurring while using a novel method, developed in accordance with the present invention, for retrieving a tool lost in a borehole.

FIGS. 4 and 5 are reproductions of recordings made from configurations of tubing, an overshot and a tool similar to the configurations shown in FIGS. 2 and 3, respectively.

DESCRIPTION OF THE INVENTION Referring to FIG. I, there is shown a conventional-type overshot retrieving device 3 lowered into a borehole S to retrieve a lost tool 7. Borehole 5 may be an open borehole or it may have a casing. Overshot 3 is lowered by adding sections of tubing 10. When it is believed that overshot 3 is over tool 7, overshot 3 is rotated to engage tool 7.

Overshot 3 and tubing 10 are then raised a predetermined distance as shown in FIGS. 2 and 3. An acoustical well sounder 12, which may be of the type manufactured by Associated Engineering and Equipment Company as their Model 22, includes a gun 17, a microphone I9, a recorder 24 electrically connected to microphone l9, and a Y-tube 25 connecting tubing 10 to gun l7 and microphone 19. Gun I7 is then fired causing a sound wave to travel down Y-tube 2S, tubing 10 and overshot 3, which results in reflections of the sound wave as the sound wave passes through restrictions, enlargements, or another medium. Microphone 19 picks up the reflections in Y-tube 25 and provides a corresponding electrical signal to recorder 24. Recorder 24 provides a record of the reflections which is monitored to determine if overshot 3 has engaged tool 7.

When tool 7 has been engaged by overshot 3, as shown in FIG. 2, the reflection of the sound wave causes a primary deflection in one sense in the recording provided by recorder 24 as shown in FIG. 4. When overshot 3 has not engaged tool 7, the reflection of the sound wave as it leaves overshot 3 causes a primary deflection in an opposite sense in the recording provided by recorder 24, as shown in FIG. 5. Thus the primary reflection in the recording indicates whether or not overshot 3 has engaged tool 7.

Recorder 24 provides the two different primary deflections as a result of the different phases of the reflections for the two conditions of overshot 3. When a sound wave escapes from a tube into air, as is the case when overshot 3 has not engaged tool 7, the reflection of the escaping sound wave is of one phase. When a sound wave reflects from the closed end of a tube, as is the case when overshot 3 has engaged tool 7, the reflection of the sound wave is of an opposite phase. Thus the reflections for the conditions that overshot 3 has and has not engaged tool 7 differ by and recorder 24 is afiected accordingly.

Well sounder I2 is disconnected from tubing 10 and overshot 3, tool 7, and tubing 10 are removed from the borehole when the recording by recorder 24 indicates that overshot 3 has engaged tool 7. Well sounder 12 is also disconnected from tubing 10 when the recording by recorder 24 indicates that overshot 3 has not engaged tool 7 and overshot 3 is then lowered for another attempt to engage tool 7.

Overshot 3 should have an inner diameter approximately equal to the inner diameter of tubing 10. If overshot 3 has a substantially smaller inner diameter than tubing 10, the reflection from the smaller inner diameter causes the recording by recorder 24 to indicate that overshot 3 has engaged tool 7 regardless of whether or not overshot 3 has engaged tool 7. When tool 7 is below the surface of a fluid, overshot 3 must be raised a predetermined distance above the fluids surface before tiring gun 17 otherwise the recording by recorder 24 will indicate an engagement due to the reflection from the surface of the fluid when in fact overshot 3 may not have engaged tool 7.

The method of the present invention, as heretofore described, utilizes an acoustical well sounder to determine whether or not an overshot retrieving device has engaged a lost tool in a borehole while the overshot retrieving device is still in the borehole.

What is claimed is:

l. A method for retrieving a tool lost in a borehole, which comprises the steps of inserting a retrieving device with tubing into a borehole, attempting to engage the tool with the retrieving device, withdrawing the retrieving device and tubing a predetermined distance, providing a sound wave in the tubing, monitoring the reflections of the sound wave to determine if the retrieving device has engaged the tool, and removing the tool, retrieving device, and tubing from the borehole when the retrieving device has engaged the tool.

2. A method as described in claim 1 in which the first five steps are repeated until the tool is engaged by the retrieving device at which time the last step is repeated.

3. A method as described in claim 1 in which the steps of providing a sound wave in the tubing and monitoring the reflections of the sound wave are accomplished with an acoustical well sounder.

4. A method as described in claim I in which the borehole has a casing.

5. A method as described in claim I in which the borehole is an open borehole.

6. A method as described in claim 1 in which the retrieving device is an overshot.

7. A method as described in claim 6 in which the monitoring step includes converting the reflection of the sound wave to an electrical signal which will initially increase in amplitude in one sense when the overshot has engaged the tool, and in an opposite sense when the overshot has not engaged the tool.

8. A method as described in claim 6 in which the monitoring step further includes providing an indication that the overshot has or has not engaged the lost tool in response to the electrical signal. 

1. A method for retrieving a tool lost in a borehole, which comprises the steps of inserting a retrieving device with tubing into a borehole, attempting to engage the tool with the retrieving device, withdrawing the retrieving device and tubing a predetermined distance, providing a sound wave in the tubing, monitoring the reflections of the sound wave to determine if the retrieving device has engaged the tool, and removing the tool, retrieving device, and tubing from the borehole when the retrieving device has engaged the tool.
 2. A method as described in claim 1 in which the first five steps are repeated until the tool is engaged by the retrieving device at which time the last step is repeated.
 3. A method as described in claim 1 in which the steps of providing a sound wave in the tubing and monitoring the reflections of the sound wave are accomplished with an acoustical well sounder.
 4. A method as described in claim 1 in which the borehole has a casing.
 5. A method as described in claim 1 in which the borehole is an open borehole.
 6. A method as described in claim 1 in which the retrieving device is an overshot.
 7. A method as described in claim 6 in which the monitoring step includes converting the reflection of the sound wave to an electrical signal which will initially increase in amplitude in one sense when the overshot has engaged the tool, and in an opposite sense when the overshot has not engaged the tool.
 8. A method as described in claim 6 in which the monitoring step further includes providing an indication that the overshot has or has not engaged the lost tool in response to the electrical signal. 